Microwave dielectric properties of high-entropy [(Mg1/2Zn1/2)0.4+x(Ni1/3Co1/3Mn1/3)0.6-x]2TiO4 ceramics

Abstract

In this study, a series of high-entropy [(Mg_1/2Zn_1/2)_0.4+x(Ni_1/3Co_1/3Mn_1/3)_0.6-x]₂TiO₄ (expressed as MZNCMT) (0.0 ≤ x ≤ 0.6) ceramics were prepared via the solid-state reaction, the high-entropy ceramics exhibited inverse spinel structure. The phase compositions, microstructures, and microwave dielectric properties were investigated. The results of x-ray diffraction (XRD) showed that a principal phase of [(Mg_1/2Zn_1/2)_0.4+x(Ni_1/3Co_1/3Mn_1/3)_0.6-x]₂TiO₄ ceramics, whereas the second phase of (Mg, Zn, Ni, Co, Mn)TiO₃ appeared when x ≤ 0.4. With the increase of x value, the relative density of the sample decreased, the unit cell volume first decreased and then kept expanding. This phenomenon could be attributed to the reduction of (Ni_1/3Co_1/3Mn_1/3)²⁺. Good microwave dielectric properties were achieved: x = 0.0 (ε_r = 17.17, Qf = 16500 GHz, τ_f = -33 ppm/℃), x = 0.5 (ε_r = 16.30, Qf = 53900 GHz, τ_f = -30 ppm/℃) and x = 0.6 (ε_r = 16.26, Qf =110800 GHz, τ_f = -39 ppm/℃), well temperature coefficient of resonance frequency (τ_f) = -30 ppm/℃ for the sample at x = 0.5, and the highest quality factor (Qf) = 110800 GHz for the sample at x = 0.6. The ε_r value of MZNCMT ceramics is consistent with the theoretical dielectric constant (ε_theo), indicating that ε_r is mainly based on ion polarization. The Qf value were highly related to the packing fraction. Furthermore, the τ_f value depended on the bond strength of A-site.